This invention relates to a switch assembly for a dynamoelectric machine, and more particularly to a starting switch assembly for a fractional horsepower induction electric motor.
Typically, capacitor start and split phase induction motors have a run winding and a starting or auxiliary winding placed in winding receiving slots provided in the bore of the stator core of the motor. The starting winding is energized during start-up of the motor (or when the speed of the motor falls below a specified operating speed) so as to create a rotating field in the stator and to apply sufficient torque to the rotor for starting purposes. However, once the motor has accelerated to a desired operating speed (e.g., about 80 pecent or more of the normal operating speed of the motor), the rotor is able to follow the alternations of the magnetic field created by the run windings, and the starting winding is no longer needed. Typically, the starting winding is not intended for continuous use and may fail if not de-energized during normal operation of the motor. As is conventional, a switch, referred to as a motor starting switch, is provided in the motor for energizing the starting winding only during start-up of the motor and for de-energizing the starting winding once the motor has attained its desired operating speed. These motor starting switches are conventionally actuated by a centrifugal actuator mounted on and rotatable with the rotor shaft of the motor, the centrifugal actuator being responsive to the speed of the motor for changing the starting switch from its start to its run state in response to the motor attaining a predetermined operating speed. Centrifugal actuators typically include an actuator member movably movable axially on the rotor shaft from an off or stop position when the motor is stopped (or is operating below a specified operating speed) to a run position upon the motor accelerating to a predetermined operating speed. Typically, an actuator linkage operatively interconnects the motor starting switch and the actuator member of the centrifugal actuator. A centrifugal actuator is shown and described in co-assigned U.S. Pat. No. 4,242,607. Motor starting switches are shown and described in co-assigned U.S. Pat. No. 4,240,001, 4,296,366, and 4,473,789.
During the service life of a motor, end play (i.e., axial movement) of the rotor shaft with respect to the end shields (or the frame) of the motor may develop. This end play may be sufficient so as to appreciably change the relative position of the centrifugal actuator (mounted on the rotor shaft) and the motor starting switch (rigidly mounted on the frame or end shield of the motor), thus affecting operation of the motor starting switch. Under certain end play conditions, the centrifugal actuator could fail to de-energize the starting winding upon the motor attaining its desired operating speed, which could eventually cause the starting winding to fail. Under other end play conditions, the centrifugal actuator may fail to re-set the motor starting switch to energize the starting winding upon subsequent start-up of the motor, and the motor would fail to start.
Also, in certain motor applications (e.g., in a clothes dryer) in which the motor starting switch is exposed to lint-laden air, the deposit of the lint within the switch has heretofore been a problem. More specifically, the motor starting switch is typically installed in the location within the motor proximate the motor bearing lubrication system, and oil vapor is oftentimes deposited on all the exterior surfaces of the switch, including the actuating plunger. Once such lint entered the housing of the starting switch, it would collect on various electrical components within the switch and could, on occasion, prevent good contact between the electrical contacts within the switch. This could cause intermittent or improper operation of the switch and possibly result in failure of the motor to start. The problem of lint and oil vapor requires that the motor starting switch be enclosed in a housing, but such switches are normally installed in a place where space is very limited. Thus, the restrictions on the size of the housing are severe.
In addition to the switch which controls the starting winding, it is also desirable in many applications to have one or more sets of auxiliary contacts to provide control signals or the like for the particular apparatus which incorporates the motor. Preferably, these control signals could occur simultaneously with the switching in or out of the starting winding. Such auxiliary contacts must also be protected from the problems of lint and oil vapor and necessarily increase the size of the starting switch assembly.
Heretofore, actual construction of motor starting switches as described above was relatively complex due to the strict requirements in terms of space, number of contacts, protection of the contacts from foreign matter, and the complexity of the apparatus itself.
One of the objects of this invention is to provide a motor starting switch assembly which is relatively insensitive to end play of the rotor shaft and which need not be accurately positioned with respect to the centrifugal actuator during manufacture of the motor.
Another object of this invention is to provide a motor starting switch assembly which substantially reduces the entrance of lint and other airborne contaminants into the interior of the switch.
Another object of this invention is to provide such a starting switch assembly which is compact in size and rugged in construction, which is reliable in operation, which is easy to install in the motor, and which has a relatively long service life.
Another object of the present invention is to provide such a motor starting switch which is easy to assemble.
Another object is to provide a motor starting switch assembly which requires no adjustment of the switch assembly itself.
Other objects and features of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.